1. Field of the Invention
The present invention relates to a cross joint used for a steering apparatus for, e.g., a vehicle.
2. Related Background Art
In the steering apparatus for the vehicle, a cross joint constructed of a pair of yokes and a cross-shaped spider and serving to propagate a torque in a way that rotates a predetermined bending angle, is interposed between, for instance, an upper shaft and a lower shaft of a steering shaft.
According to a cross joint disclosed in, e.g., Japanese Patent Application Laid-Open No. 2000-170786, a shaft member of the spider is fitted into a bearing hole of a yoke through a needle bearing, such that said shaft member is capable of oscillating. A spherical protrusion formed on an axial core of an inner surface of a cup of the needle bearing is fitted into and kept in contact, by pressure, with a conical hole formed in the axial core of the spider shaft.
With this configuration, even when vibrations are propagated from wheels, a minute gap between the spider shaft and the needle bearing is kept uniform, thereby preventing an emission of noises due to an interference between the spider shaft and the needle bearing.
According to the structure disclosed in Patent Application Laid-Open No. 2000-170786, however, if a dimensional accuracy of each component is low, when the cross joint is assembled to the yokes, it is difficult to bring the spherical protrusion provided on the inner surface of the cup of the needle bearing into contact with the conical hole of the spider shaft with a proper pre-load. As a result, a minute gap between the spider shaft and the needle bearing can not be kept uniform, resulting in an emission of noises due to an interference therebetween.
On the other hand, if the dimensional accuracy of each component is enhanced, though capable of preventing the emission of noises, a rise in manufacturing cost is brought about as a negative aspect.
Further, when a steering shaft of the vehicle is steered, a steering wheel is rotated, with the result that the spider shaft is oscillated. An angle of this oscillation is determined by a joint fitting angle in the vehicle and is on the order of ±30 degrees in the case of an ordinary car. The rollers of the needle bearing smoothly rotate owing to the oscillations of the spider shaft.
According to Japanese Patent Application Laid-Open No. 2000-170786, however, the axial core of the roller is not parallel but inclined to the axis of the spider shaft in many cases, and the roller, with its rotation, moves in the axial direction within the cup of the needle bearing. With the movement of the roller in the axial direction, the roller comes into contact with the cup wall, and sliding contact occurs between the roller and the cup wall. As a result, a bending torque of the steering shaft increases, and a smooth feeling of steering can not be obtained.